1. Field of the Invention
This invention relates to meltable-matrix support of workpieces from which slender structural elements are machined, and particularly to procedures for machining such workpieces.
2. Description of Related Art
Programmed milling machines are conventionally utilized to mill workpiece blanks, such as forgings, castings, bars or plate, to as close to final contour as the capability of the machine and the manner it supports the workpiece will permit. Workpieces may be clamped at localized points; if so the workpieces may flex so markedly under the forces of machining as to defy machining to final contour. Extreme warping of castings and forgings during machining may also occur when "locked in" stresses (those attendant to cooling) are relieved as one surface is machined and released preliminary to reclamping for machining an opposite surface; such warping makes it virtually impossible to machine the opposite surface to final contour in a single programmed operation. Also, the surface areas obstructed by clamps cannot be machined without reclamping the workpiece at other points.
Matrix support during machining is shown in the prior art as applied to machining airfoil-shaped turbine blades. A blade blank is first supported by embedding one adhesive-coated surface in the meltable matrix of a first pallet; then, after machining the opposite surface and coating it with adhesive, a second meltable matrix pallet receives and embeds such opposite surface at a programmed spacing from the first pallet. The matrix of the first pallet is then melted away to permit machining of the theretofore embedded surface.
By this procedure the workpiece is prevented from flexing as "locked in" stresses are released during the first machining. The procedure is disclosed in U.S. Pat. Nos. 3,790,152, 4,629,378 and 4,730,382, the latter two patents showing a chucking center which, among its other functions, sets the precise spacing of such pallets from each other for transfer of the workpiece so that an integrated machining program may proceed to completion.